Losing Castonzo would be another big blow to an offense that is already without Andrew Luck, who is expected to miss most of the rest of the regular season with a lacerated kidney and partially torn abdominal muscle.

The offensive line has struggled to protect Luck and his replacement, Matt Hasselbeck, even though the 40-year-old Hasselbeck improved to 3-0 with Sunday’s win at Atlanta. Castonzo has been the one consistent performer on the line. He had started 66 consecutive regular-season games and signed a four-year, $43.6 million contract extension in September.